A safety mechanism stands for a mechanism which when a tip of the clip is lifted up in a state where the pen point of the refill is at the writing position protruding beyond the end of the holder, the pen point draws back into the holding position in the holder. By this mechanism, clothing will not be stained in case the writing instrument is inserted in, for example, a chest pocket of a clothing with the pen point staying out at fault.
Several types of knock-type writing instruments are known. One of them is a Kahn knock-type writing instrument in which if a knocking operation is carried out with the pen point in the writing position and the knock rod is released (hereinafter referred to as “return operation”), a rotor is pushed back by the force of a spring, and a cam protuberance 3b′ of the rotor moves vertically along an inner cylinder cam 2b′ (over a distance a, in the axial direction only) to place the pen in a pen point-holding position (see FIG. 11).
However, due to the above vertical motion of when the knock is released (return operation), a shock is imparted to a refill (ink container). When the refill contains an aqueous ink or a gel ink, in particular, the ink in the refill can be displaced or leak out, whereby air may become trapped in the end of the refill which can result in blurred writing. Therefore, it has been desired to devise a mechanism to reduce the shock caused by the vertical motion.
With a Kahn knock-type writing instrument equipped with a safety function, the writing position is maintained as the tip of the clip is engaged to limit the motion of the rotor. In the return operation, the cam protuberance 3b′ of the rotor vertically moves along the inner cylinder cam 2b′ (by a distance a, in the axial direction only) to establish the pen point-holding position, like an ordinary Kahn knock-type instrument. Here, if the safety release operation is effected (hereinafter referred to as “safety operation”) by lifting up the tip of the clip, however, the motion of the rotor is no longer limited, and the cam protuberance of the rotor vertically moves up to the pen point-holding position. In the case of a cam constitution shown in FIG. 12, for instance, a cam protuberance 3b′ vertically moves (distance i) together with a slide body 6a′. 
A shock is imparted to the refill (ink container) even by the collision of when the cam protuberance vertically moves during the safety operation giving rise to the occurrence of the problem described above. Therefore, it has been desired to provide a mechanism for relaxing shocks in the vertical motion.
Japanese Unexamined Patent Publication JP-A-2000-218989, on the other hand, discloses a knock-type writing instrument with safety using a spring as a buffer member.
This system, however, is accompanied by a problem of an increase in the number of parts. The aqueous ink and the gel ink have recently been frequently used, and it has been desired to solve the above inconveniences caused by shocks relying on simple systems.